<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<style type="text/css">
#a1 {
	border: 2px solid black;
	width: 70px;
	height: 50px;
	margin: 0 auto;
}
</style>
</head>
<body>
	<div id="a1">123456</div>

</body>
</html>